Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
Digital information can be exchanged between modems over an analog communication link. Typically, each modem may be configured to both: generate a modulated analog signal so as to encode digital data in the signal, and demodulate a received analog signal so as to recover digital data represented by the signal. A modem can therefore function to: (i) receive a data value and output a modulated analog signal that represents the data value, and also (ii) receive a modulated analog signal and output a data value represented by the modulated analog signal.
Some modulation techniques include: frequency modulation, in which bits of digital data are encoded in a signal in accordance with changes in the frequency of the signal; amplitude modulation, in which bits of digital data are encoded in a signal in accordance with variations in the amplitude of the signal; and phase modulation, in which bits of digital data are encoded in a signal in accordance with variations in the phase of the signal.
To send a given data value between modems, a first modem can receive a particular data value for transmission to a second modem. Then, based on the particular data value, the first modem can select an analog signal with certain identifiable parameters. The parameters are selected such that the analog signal having those parameters represents the received data value in accordance with the employed modulation technique. The first modem can then generate an analog signal having the selected parameters. The resulting modulated signal that represents the particular data value can then be mixed with a carrier frequency and transmitted over a wireless or hard-wired communication path to the second modem (perhaps in combination with an associated transmission system). The second modem can receive the signal, convert the received signal to baseband (perhaps in combination with an associated receiver system), and process the signal to identify the modulated parameters. The second modem can then, based on the identified modulated parameters, recover the particular data value and thereby complete the process of communicating the data value. In practice, both modems may have a stored database, or a hardware-implemented equivalent, that associates various data values with respective modulated parameters and thereby allows the modems to perform mappings between data values and modulated parameters.
Various communications systems may use modulated analog signals for conveying digital data over communication links. One such application may involve a cellular wireless network system. A typical cellular wireless network system (wireless communication system) may include a number of base stations with antennas that radiate to define wireless coverage areas, such as cells and cell sectors. Within the wireless coverage areas, a subscriber (or user) accesses the communication services via a wireless communication device (WCD), which can communicate by exchanging radio frequency signals with the base stations. WCDs may include cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more communication networks, such as the public switched telephone network (PSTN) and/or a wide area network (WAN) for sending and receiving packet data (the internet, for instance). These (and possibly other) elements function collectively to form a Radio Access Network (RAN) of the wireless communication system. With this arrangement, a WCD within coverage of the RAN may communicate with various remote network entities.
In general, communications on the RAN are carried out in accordance with an air interface protocol that provides procedures for coordinating communications between the base stations and the WCDs. Examples of existing air interface protocols include, without limitation, Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Long Term Evolution (LTE), Wireless Interoperability for Microwave Access (WiMAX), Global System for Mobile Communications (GSM), among other examples. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handoff between coverage areas, and other functions related to air interface communication. Similarly, communications between the base station, other network infrastructure, and various communication networks are carried out in accordance with certain protocols as well.